This review explores the biological activities of 3,5-diiodothyronine (T₂), a metabolite of thyroid hormones. T₂ stimulates mitochondrial respiration through nuclear-independent pathways, enhancing energy expenditure and oxygen consumption. It influences mitochondrial functions, including oxidative phosphorylation and fatty acid oxidation, and modulates enzymes and ion transporters. T₂ also exhibits thyromimetic effects, impacting
